I have create FHIR server which has passed almost 95% of conformance tests. but the real problem is that is there any interoperability model to implement FHIR in our existing system to communicate with different clients?
Can you explain further what you mean by an "interoperability model"?
it means how can some one communicate with our EHR system using FHIR server? As per my understanding i have to develop interface that will communicate at real time with our EHR and client , am I right?
FHIR supports multiple means of accessing data. You can expose your data as a FHIR RESTful server and allow other systems to query it. You can send (and respond to) FHIR messages. Or you can expose a FHIR services interface. RESTful services require the least negotiation and thus are typically most interoperable.